I have isolated many strains of Mesorhizobium from the nodule of Chickpea (Cicer arietinum L.) growing in the desert Thal. During summer, temperatures rise up to 50 C in Thal but bacteria survived. But in lab conditions they like to grow in 27 C. When temperature rise up to 37 C the bacteria died. I don't understand how bacteria survived in the desert Thal.
I think soil temperatures are much lower than the temperatures prevail in environment due to buffering and insulation of soil..meaning thereby the temperatures in rhizosphere are never that much high ...
I agree with Dr. Yasir Khurshid that soil acts as buffering and insulating agent that protects rhizobium from high temperature. In soil there are many factors and components that shield bacteria from high temperature. The soil surface temperature is different compared to deeper levels of soil. How did you do your soil sampling... means you took sample from the surface or by digging from top to bottom and then collected the samples? In lab conditions you provided enrichment medium to grow and that medium is in direct exposure to heat. What was the humidity/moisture level? check this too.
Also you can use sterilized soil (same soil used for isolation after autoclaving) as a growth medium for your isolate and incubate to high temperature.
one more thing.... as you mentioned you have isolated the Mesorhizobium from the nodule of Chickpea (Cicer arietinum L.) growing in the desert Thal, means your isolate is symbiotic and attached to roots of the chickpea plant. Studies reported that root exudates also helps in the growth and proliferation of the symbiotic bacteria. May be this would also be the reason for tolerating the high temperature. It is also good to notice the temperature near rhizospheric region. This helps you lot.
I am also eager to get the suggestions of other experts.
Thanks.
Ahmad, It is important to know that Mesorhizobium infect plants at 50oC. If not - bacteria survives at plant tissues because of low water content and lack of active metabolism. For instance, hot water treatment of seeds kills plant pathogenic bacteria at 48-50oC, but dry seeds must be sterilized at 80-90oC. In lab you subculture bacteria on liguid or agar medium with 95-99% of water and expect active growth in days...
See some more information at http://www.nwmo.ca/uploads_managed/MediaFiles/1708_nwmotr-2010-08_r0f_final_microibal_elevated_temperature_experiments.pdf
Thanks for suggestion, You all are right regarding soil buffering condition and nodule environment. Chickpea grow in winter and harvested in April. I think in these days there is no problem for mesorhizobium because there is lot of nutreints from plant present and also temperature is about 15 to 30 Centigrade. But my question is how bacteria survived in sand desert where temperature rise upto 50C. Sand gain temperature easily and that time there is no vegetation etc
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